A Limit on the Branching Ratio of the Flavor-Changing Top Quark Decay T→Zc

Abstract

We have used the Collider Detector at Fermilab (CDF-II) to set upper limits on the branching ratio of the flavor-changing neutral-current (FCNC) top quark decay t → Zc using a technique employing ratios of W and Z production, measured in 1.52 fb −1 of pp data. The analysis uses a comparison of two decay chains, pp → tt → W bW b → νbjjb and pp → tt → ZcW b → + − cjjb, to cancel systematic uncertainties in acceptance, efficiency, and luminosity. We validate the MC modeling of acceptance and efficiency for lepton identification over the multi-year dataset also using a ratio of W and Z production, in this case the observed ratio of inclusive production of W to Z-bosons, a technique that will be essential for precision comparisons with the standard model at the LHC. We introduce several methods of determining backgrounds to the W and Z samples. To improve the discrimination against SM backgrounds to top quark decays, we calculate the top mass for each event with two leptons and four jets assuming it is a tt event with one of the top quarks decaying to I am blessed to find so many good friends at the University of Chicago, I highly treasure all the time spent together. I thank

Search for anomalous production of multiple leptons in association withWandZbosons at CDF

“…The DIF algorithm requires the χ 2 per degree of freedom of the fitted track to be less than 3 and requires that the impact parameter of the track be less than 0.02 cm. Additionally, for tracks with p T > 300 GeV, it requires N transitions > 30, where N transitions is the number of times the pattern of track hits crosses the fitted track [25]. Muons consistent with cosmic rays are vetoed [26].…”

Search for anomalous production of multiple leptons in association with W and Z bosons at CDF

“…The DIF algorithm requires the χ 2 per degree of freedom of the fitted track to be less than 3 and requires that the impact parameter of the track be less than 0.02 cm. Additionally, for tracks with p T > 300 GeV, it requires N transitions > 30, where N transitions is the number of times the pattern of track hits crosses the fitted track [25]. Muons consistent with cosmic rays are vetoed [26].…”

A Search for Anomalous Production of Events with Multiple Leptons and a $W$ or $Z$ Boson

“…The DIF algorithm removes these tracks by requiring the χ 2 per degree of freedom of the track fit to be less than 3 and the impact parameter of the track to be less than 0.02 cm. Additionally, for tracks with Tight Central Electron Selections η Detector ≤ 1.1 Track must be fiducial to CES Table 4.1: Selections to identify tight central electrons p T > 300 GeV, it requires N transitions > 30, where N transitions is the number of times the pattern of track hits crosses the fitted track [28]. Muons consistent with cosmic rays are vetoed [29].…”

“…The ratio of W to Z production is a very precise test of problems in lepton trigger efficiencies, lepton identification efficiencies, or problems with E T [28]. This ratio is calculated in each differently-triggered dataset, and the deviation from the theoretical value of R = 10.67 [27] is used as a systematic uncertainty on the trigger efficiency.…”